Over time, the repeated normal use of electrical equipment causes electrical connections to become loose and weak. The increased electrical resistance of such connections can result in heating which represents a fire hazard. The heating itself causes further increased electrical resistance and increased heating which can promptly lead to catastrophic failure. Insurance and utility companies have recommended guidelines that establish temperatures which indicate that corrective action should be taken. Infrared inspection has been used as a fast, easy and effective way of detecting electrical problems by the heat generated. Infrared inspection is safe as no contact is made with the electrical equipment. It is cost effective and accurate as the equipment is not shut down.
One form of infrared inspection is through the use of infrared thermal imaging. A less expensive approach is use of a hand-held scanner such as described in U.S. Pat. No. 4,874,253, incorporated herein by reference. Disadvantages of those test methods are that they are only carried out periodically, so there is a risk of failure between periodic checks. Continuous monitoring, particularly of critical components of the system, has been carried out using inexpensive thermopile sensors mounted to the electrical equipment. Such sensors are described in U.S. Pat. Nos. 5,229,612, 5,319,202 and 5,333,784, all incorporated herein by reference in their entireties. As disclosed in FIG. 1A of U.S. Pat. No. 5,229,612, the sensor may be a simple thermopile with a calibrating resistor, or as illustrated in FIG. 1B, it may include thermocouple leads to emulate a thermocouple sensor. To minimize electrical interference, the sensor housing is preferably of non-conductive plastic material. A plastic Fresnel lens may be utilized to enable more distant viewing such as up to 32 cm. The plastic reduces expense and the Fresnel lens reduces the thickness and thus energy absorption. Use of infrared sensors as monitors has been described by Pompei and Kennedy in “Hunting of the Mighty Milliwatt—The Next Technology Step,” June 2006, and Pompei and Kennedy, “Hunting Might Milliwatts,” June 2006, both of which were included in the provisional application 61/428,649 and are incorporated herein by reference in their entireties.